Tibial plateau leveling osteotomy plate

ABSTRACT

An improved tibial plateau leveling osteotomy plate is disclosed. The plate is contoured in its proximal head portion to more closely resemble the structure of the tibial bone segment that is cut and rotated during the procedure. The plate also preferably has screw holes in the proximal head portion that are machined through the pre-contoured proximal head portion and are designed to angle the screw in a targeted screw path with respect to the osteotomy.

TECHNOLOGY FIELD

The present invention relates to surgical plates for fixing two separatebone segments and methods for using the plates. More specifically, theplates can be used for tibial plateau leveling osteotomy procedures,particularly for use with canines.

BACKGROUND OF THE INVENTION

Tibial plateau leveling osteotomy (TPLO) procedures are well known inthe veterinary art. Tibial plateau leveling osteotomy procedures areused to correct ruptured cranial cruciate ligaments for various animals,primarily for canines. These procedures provide an alternative therapyto ligament repair procedures. Today, tibial plateau leveling osteotomyprocedures have become the standard of care for medium and largecanines.

By way of background, the cranial cruciate ligament stabilizes thecanine's stifle joint (called the knee for humans). One of the importantfunctions for the ligament is to control the sliding of the upper femurbone on the lower tibia bone. Unfortunately, however, for many caninesthe ligament partially or fully ruptures. The tibial plateau levelingosteotomy procedure provides a way to correct this problem.

The tibial plateau leveling osteotomy procedure is well documented inthe art. For example, the procedure is described in U.S. Pat. Nos.4,677,973 and 5,304,180, both of which are incorporated herein in theirentirety. The procedure is also described at the web sitewww.vetsurgerycentral.com/tplo. Basically, a curvilinear cut is made tothe upper portion of the tibia. This cut portion of the tibia is thenrotated on the order of about 20-30 degrees thereby creating a morelevel plane or surface on the top of the tibia upon which the femur canrest. The cut and repositioned portion of the tibia is then secured tothe lower portion of the tibia.

Various means have been used to fix and secure the cut portion of thetibia to the remaining portion of the tibia. Initially, screws and wirewere used for this purpose. Later, those in the art used metal platesthat were anchored into the tibia in both the bottom portion and upper,cut portion by way of bone screws. The problem with many platescurrently in use is that they require the surgeon to manipulate theplate to conform to the tibia during the surgical procedure. This isoften difficult because the plates are relatively thick and rigid, andthus are not easily bent into an acceptable shape. Furthermore, bendingof the plate during the procedure can result in the screw holes becomingdeformed.

Another drawback with the TPLO plates currently available is that thescrew holes in the plate for use with the upper, cut portion of thetibia are not designed for optimum fixation. Improved designs for screwplacement into the tibia are needed to avoid the screws from beinglocated near a cut portion of the tibia or near the articular surface ofthe tibia and the femur.

SUMMARY OF THE INVENTION

The present invention provides a bone plate designed to secure twotibial bone segments of an animal as part of a tibial leveling osteotomyprocedure for an animal. The invention also provides for methods ofusing the bone plate during such procedures and for kits containing thebone plate and associated materials.

In one embodiment, the bone plate has a distal portion comprising anelongated shaft having disposed therein a plurality of distal portionscrew holes each designed to accept a screw. The screws can be of anytype used in the art, such as locking screws, cortex screws, andcancellous screws. The bone plate has a proximal portion having an uppersurface and a bone-contacting surface opposite the upper surface. Thebone-contacting surface is pre-contoured to be configured anddimensioned to conform to a tibial bone segment and is partially definedby a cylinder. The arched surface of the cylinder that defines at leasta part of the bone-contacting surface for the proximal portion of theplate can have varying dimensions depending on the anatomy in which itis to be used. The proximal portion contains a plurality of proximalportion screw holes that are machined through the pre-contouredbone-contacting surface and that are designed to accept a locking screw.By machining these screw holes through the pre-contoured bone-contactingsurface, the screw holes define a pre-determined and targeted screw paththrough the tibial bone segment.

The targeted screw path for the proximal portion screw holes providesvarious advantages for the bone plate. The screws can have screw pathsthat are targeted to avoid the articular surface between the tibia andthe femur, to avoid the osteotomy surface of the tibia, and to avoid theouter surface of the tibia, and thus to enter into the tibia through thearea of relatively more bone mass.

In one embodiment, the proximal portion has at least three locking screwholes arranged such that there is a superior, proximal screw hole and acranial and a caudal screw hole that are both distal from the superiorscrew hole. Preferably, the superior screw hole is designed such thatthe superior screw will be angled distally from the bone-contactingsurface and also preferably caudally. Preferably, the cranial screw holeis designed such that the cranial screw will be angled caudally from thebone-contacting surface. Also preferably, the caudal screw hole isdesigned such that the caudal screw will be angled cranially from thebone-contacting surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purpose of illustrating theinvention, there is shown in the drawings embodiments that are presentlypreferred, it being understood, however, that the invention is notlimited to the specific methods and instrumentalities disclosed. In thedrawings:

FIG. 1 is a top view of an exemplary bone plate;

FIG. 1A is a side, cross sectional view of an exemplary bone plate;

FIG. 1B is a side, cross sectional view of an exemplary bone plate andscrew;

FIG. 2 is a side view of an exemplary bone plate;

FIG. 2A is a cross sectional view along the distal portion of anexemplary bone plate;

FIGS. 2B-2D are end, side, and top views, respectively of an exemplarybone plate;

FIG. 3 is a proximal end view of an exemplary bone plate;

FIG. 4 is a rotated proximal end view of an exemplary bone plate;

FIG. 4A is a top view reflecting the rotation axis of FIG. 4;

FIG. 5 is a rotated proximal end view of an exemplary bone plate;

FIG. 5A is a top view reflecting the rotation axis of FIG. 5;

FIG. 6 depicts the cylindrical surface of the bone-contacting surface ofan exemplary plate;

FIG. 7 is a perspective view of an exemplary bone plate with proximalhead screws;

FIG. 8 is an end view of an exemplary bone plate with proximal headscrews;

FIG. 9 is a side view of an exemplary bone plate with proximal headscrews;

FIG. 10 is a top view of an exemplary bone plate;

FIG. 11 is a top view of a relatively larger exemplary bone plate;

FIG. 12 is a top view of a relatively larger exemplary bone plate;

FIG. 13 is a top perspective view of the top of the articular surfacebetween the tibia and the femur with an exemplary bone plate affixed tothe tibia; and

FIG. 14 is a side perspective view of an exemplary bone plate affixed tothe tibia.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The various features of the tibial plateau leveling osteotomy platesdisclosed herein can be described by reference to the drawings. Forexample, FIG. 1 depicts an exemplary embodiment of the presentinvention. The plate 10 has two distinct portions—a lower or distalportion 12 and an upper or proximal portion 14. These two portions arepreferably formed integral to one another, but could be made of twoseparate portions attached by conventional means. It is most preferredthat these two portions be made from the same piece of metal, preferablysurgical grade stainless steel, such as 316L implant grade stainlesssteel.

The plate 10 is designed for attachment to the tibia of an animal, suchas a canine, feline, bovine, equine, but more particularly for canines,during a tibial plateau leveling osteotomy procedure. The lower ordistal portion 12 is designed to be affixed to the lower or distalportion of the tibia. The upper or proximal portion 14 is designed to beaffixed to the upper or proximal portion of the tibia that has been cutand repositioned during the procedure. The plate 10 thus fixes therelative positions of the substantially curvilinear cut and rotatedtibial bone segments.

The plate 10 is secured to the tibial bone segments by screws. Asdepicted in FIG. 1, the distal portion 12 for this example can bedescribed basically as an elongated shaft, that as shown in FIG. 2, hasa length, L, substantially greater than its depth, D, and its width, W.As shown, the lower portion has three screw holes 16 for fixing theplate 10 to the tibia, however more or less screw holes can be used. Thescrew holes 16 can be of any design used in the field for fixing platesto bones in animals. Examples of screw hole 16 designs are set forth inU.S. Pat. Nos. 5,002,544; 5,709,686; 6,669,701; 6,719,759; and Re31,628, each of which is incorporated herein in its entirety byreference. For example, as shown in FIG. 1, the holes 16 are designed aselongated slots, with the longer axis being parallel to the longitudinalaxis of the plate 10. As depicted for this particular embodiment, thetwo outer holes 16 define first and second dimensions on bone-contactingsurface 22. First dimension, D_(L) (parallel to plate longitudinal axis)is longer than second dimension D_(Q) (perpendicular to longitudinalplate axis).

The holes 16 are preferably dynamic compression screw holes, whichpromote healing of the bone. These holes can be shaped to have a concaveand preferably partially spherical recess 19 defined by first outerperiphery 17 defining the cut into the upper surface 20 of the plate 10,and a second inner periphery 18 that is narrower than the outerperiphery 17 in both the parallel and perpendicular directions from thelongitudinal plate axis. As seen in FIGS. 1A-1B, it is preferred thathole 16 be designed such that it provides for compression in thedirection toward the osteotomy by having an inclined surface 13 at thedistal end of the hole 16 such that a bone screw can be positioned tocompress the bone toward the osteotomy site when the screw is advancedand makes contact with the inclined surface. The hole 16 also has asubstantially spherical surface 15 opposite the inclined surface 13. Therecess 19 is dimensioned to receive a bone screw having an undersidehead portion that is spherical-shaped, or substantially spherical-shapedand where the underside of the screw head is designed to rest upon therecess 19. Thus, screws placed in the distal portion of hole 16 willhave a compression force and screws placed in the middle or proximalportions of the hole 16 will have a neutral compression force. Screwssuch as cortex and cancellous screws can be used with the holes 16.

The distal portion 12 of the plate 10 can also contain one or more holes16 a that is a combination hole defined by walls having a threaded and anon-threaded portion. The combination hole 16 a has a threaded portion21 that extends over a first angle 23 with respect to at or near theupper surface 20 and a second angle 24 with respect to at or near thebone-contacting surface 22. The first angle preferably extends betweenabout 170° and 230° and the second angle preferably extends betweenabout 225° and 275°. The screw to be used with combination hole 16 a canbe a locking or bone, such as a cortex, screw. A locking screw hasthreads on the underneath side of the head that engage in mating threadsin the wall of the hole to lock the screw into place in the plate. Useof a locking screw secures the head of the screw to the plate 10 formaintaining a fixed angular relationship between the locking screw andthe plate. Cortex screws are designed to go through relatively harderbone mass and have relatively tighter thread patterns. Use of bothlocking screws and non-locking screws provides stability between boththe screw and the bone plate and between the bone plate and the bone asdescribed in U.S. Pat. No. 6,623,486, which is hereby incorporated inits entirety by reference.

As depicted in FIG. 1, the plate 10 contains screw holes in the proximalportion 14 to secure the plate 10 to the cut and rotated portion of thetibia. As shown, there are preferably three holes in the proximalportion 14—a superior hole 30, a cranial hole 31, and a caudal hole 32located near the edge 36 of the proximal portion. These holes arepreferably conical shaped holes that are threaded to receive threaded,locking bone screws. Preferably, at least one, and more preferably all,of these holes are designed such that the threads 33 engage threadslocated on the underneath of the head of the screw, which threads are ofa different dimension than those along the shaft of the screw. Thus, theholes 30, 31, 32 are preferably designed to be used with locking screws.Although it is preferred that the holes 30, 31, 32 be designed to beused with locking screws, these holes can also be designed to be usedwith any conventional bone screw such as cortex and cancellous screwswith any known screw hole design.

The types of screw holes are shown in cross-section in FIGS. 1A-1B. Asshown in FIG. 1A, hole 16 a can be a combination hole as described abovehaving threads along a partial portion of the hole wall. Representativehole 30 is shown as having threads preferably around the 360°circumference of the hole at its lower portion to engage the undersideof the head portion 38 of superior screw 30 a.

As shown in side view FIG. 2, the proximal portion 14 is pre-bent suchthat it is contoured to at least partially conform to the anatomy of thetibial bone segment that has been repositioned during the TPLOprocedure. Thus, the proximal portion 14 is in a different plane thanthe distal portion 12. It is preferred that the proximal portion 14 bepre-bent or manufactured to fit or contour to the bone anatomy prior tohaving the screw holes (for example, holes 30, 31, 32) in the proximalportion 14 machined therein. In this way, as seen below, the screw holescan be made to receive locking screws that when screwed into place havea fixed path through the bone structure. The present invention providesfor optimized screw paths for the screws in the proximal portion 14 sothat the screws avoid the articular surface and the osteotomy surface.

As also shown in FIG. 2, the distal portion 12 preferably containsrecesses 26 defined by walls 26 a so that when the plate is implantedthere is a space between the tibia and the plate 10. Such recesses aredisclosed in U.S. Pat. No. 5,002,544, which is hereby incorporated inits entirety by reference for this feature. The recesses 26 can takevarious dimensions but are essentially designed to provide a relativelysmall space between the bone-contacting surface 22 and the bone.Preferably, the recesses are formed by cutting a conical shape into theunderside of the plate. As shown in FIG. 2 a, the recesses can bedescribed as forming an angle α between the bone-contacting surface 22.The angle can be defined by the beginning point of the recess 27 and itsending point 28 and the plane defined by the bone-contacting surface 22.The angle can be between about 10° and about 30°. Preferably therecesses 26 are off-set distally from the center of the holes 16 and arepreferably located in parallel on both sides of the plate 10 as shown inFIG. 2 a.

The proximal portion 14 of the plate 10 is designed or configured in itsdimensions to advantageously contour to the tibial bone segment that hasbeen cut and rotated during the TPLO procedure. This feature can be morereadily explained in the preferred embodiment by first defining threeorthogonal planes with respect to the plate 10 as shown in FIGS. 2B-2D.In FIG. 2B, the plate 10 is viewed from the end of the distal portion 12longitudinally along its shaft. A base plane 42 is defined by the flatdistal portion 12 at the bone-contacting surface 22. A mid-plane 44 isdefined as bisecting the base plane in the distal portion 12 of theplate 10 and extending along the length of the plate. A transverse plane46 is defined as being orthogonal to the base plane 42 and the mid-plane44.

As shown in FIG. 3, the plate 10 is shown in view looking down itslength from the end of the proximal portion 14. Center lines 34 denotethe center axis of the holes 30, 31, and 32. These center lines 34 arepreferably off-set from the mid-plane 44 for the proximal portion 14 asdescribed below. The center lines 34 also depict the targeted screwpaths for the locking screws. The targeted screw paths are determined bythe threads contained on the walls of the holes 30, 31, and 32 that areengaged by the mating threads 38 on the underside of the head of thelocking screws as depicted in FIG. 1B.

The contoured shape of the bone-contacting surface 22 of the proximalportion 14 can be more readily viewed by rotating the plate 10. Thepreferred contour for the bone-contacting surface 22 of the proximalportion 14 is that formed by an arc of a cylinder. The centerline of thecylinder can be viewed perpendicularly by rotating the plate twice.First, the plate 10 can be rotated about 5-15°, preferably about 7-13°,more preferably about 10° in a clock-wise fashion about a first rotationaxis 48 that is defined by the intersection of the mid-plane 44 and anoff-set transverse plane 46. The result of the first rotation is shownin FIG. 4 and the rotation axis 48 is shown in FIG. 4A. As shown in FIG.10, the off-set transverse plane 46 defining first rotation axis 48 islocated about 18-30 mm, preferably about 21-27 mm, and more preferablyabout 24 mm distally from the center axis of superior hole 30 and thedistance is depicted by line 30 _(L) (where the center axis for hole 30is defined by the intersection of the hole axis with the top surface ofthe plate). Next, the plate 10 is rotated about 15-30°, preferably about20-25°, and more preferably about 23.5° downward about a second rotationaxis 49 defined by the intersection of the off-set, rotated, transverseplane and the base plane 42. The result of the second rotation is shownin FIG. 5 and the rotation axis 49 is shown in FIG. 5A. This rotationresults, as shown in FIG. 6, with the bone-contacting surface 22 ofproximal portion 14 being defined by cylinder 29 that has its centeraxis 40 perpendicular to the page after the rotations. The radius 42 ofthe cylinder 29 is about 18 to about 24, preferably about 20 to about22, and more preferably about 21 mm and thus defines the arched andcontoured bone-contacting surface 22 for the proximal portion 14 of theplate 10.

The plate 10 is also preferably designed to have the screws for theproximal portion 14 angle into the tibia so that the screws are directedaway from the articular surface between the tibia and the femur, awayfrom the osteotomy surface of the tibia, and away from the edges of thetibia and into the central mass of the tibia. Preferably, the superiorscrew hole 30 is angled such that the superior screw 30 is angled awayfrom the articular surface where the femur and tibia contact. Also,preferably the cranial and caudal screw holes are angled such that thecorresponding screws are angled away from the edges of the tibia andaway from the cut portion of the tibia from the osteotomy. Thus, theplate 10 is designed to have optimal screw paths for the screws usedwith the superior 30, cranial 31, and caudal 32 screw holes. The optimalscrew paths are preferably achieved by first shaping or pre-contouringthe proximal portion 14 of the plate 10 to substantially conform to thebone anatomy and then machining the screw holes through thepre-contoured proximal portion 14. The use of a screw hole designed foruse with a locking screw results in the screw path taken by the lockingscrew being fixed so that the resulting screw path is targeted through adesired section of the tibial bone segment.

FIGS. 7-9 depict one embodiment for the design of these screw paths. Asshown in FIG. 8, looking down the shaft from the proximal end thesuperior hole 30 is designed such that the center axis 34 for the screwpath is angled about 5° from the mid-plane 44. The center axis 34 forthe superior hole 30 for the superior screw 30 a can be angled betweenabout 2° and about 10°, and preferably between about 3° and about 7°. Asshown, the cranial hole 31 is designed such that its center axis 34 forthe cranial screw 31 a is angled about 5° from the mid-plane 44. Thecenter axis 34 for the cranial hole 31 for the cranial screw 31 a can beangled between about 2° and about 10°, and preferably between about 3°and about 7°. As shown, the caudal hole 32 is designed such that itscenter axis 34 for the caudal screw 32 a is angled about 3° from themid-plane 44. The center axis 34 for the caudal hole 32 for the caudalscrew 32 a can be angled between about 1° and about 7°, and preferablybetween about 2° and about 5°.

The proximal portion 14 screw holes 30, 31, 32 can also be angled suchthat the superior 30 a, cranial 31 a, and caudal 32 a screws are notperpendicular to the base plane 42. Again, the advantage for such adesign is to angle the screws so that they enter an area of greater bonemass in the tibial bone segment that was cut and rotated during the TPLOprocedure. In the embodiment illustrated, as seen in FIG. 9, thesuperior hole 30 is designed such that the center line 34 for the holeis at an angle of about 93° to the base plane 42. This results in thesuperior screw 30 a being angled distally or inwardly toward the centerof the proximal portion 14 of the plate 10. The superior hole 30 can bedesigned such that its center line 34 is at an angle of between about91° and about 97°, preferably between about 92° and about 95° from thebase plane 42, but it can also be at an angle of 90°. As illustrated,the cranial 31 and caudal 32 holes are at an angle of 90°, orperpendicular, to the base plane 42, however either or both of theseholes can be designed such that their center lines 34 are at an anglebetween about 85° and about 89°.

As illustrated, the proximal portion 14 of the plate preferably containsthree screws, however the plate can be designed with more or lessscrews, such as 2-4 proximal-head screws. It is preferred that thecranial screw hole 31 and caudal screw hole 32 be positioned distallyfrom the superior screw hole 30. All screw hole dimensions are takenfrom the points defined by the intersection of the hole axis with thetop surface of the plate as depicted by axis points 35 as shown in FIG.10. Preferably the center of cranial screw hole 31 will be positioned adistance of between about 3.5 mm and about 6 mm, preferably about 4 mmto about 5.5 mm, and more preferably about 4.5-5 mm distally fromsuperior hole 30 and parallel to mid-plane 44 as shown by line 30-31_(L). Also preferably, the center of caudal screw hole 32 will bepositioned a distance of between about 6 mm to about 9 mm, preferablyabout 7 mm to about 8 mm, and more preferably about 7.3-7.7 mm distallyfrom the superior hole 30 and parallel to mid-plane 44 as shown by line30-32 _(L).

The head portion 14 screw holes can also be positioned off of themid-plane 44. Superior screw hole 30 can have its center positionedeither on the mid-plane 44, or preferably it is positioned between about0.5 mm and about 3 mm, preferably about 1.2 to about 2.4 mm, and morepreferably about 1.6-2 mm perpendicularly and cranially from themid-plane 44 as shown by line 30 _(W). The cranial screw hole 31 ispreferably positioned such that its center is between about 4 mm andabout 6.5 mm, preferably between about 4.5 mm and about 6 mm, and morepreferably about 5-5.5 mm perpendicularly and cranially from thesuperior hole 30 as shown by line 30-31 _(W). The caudal screw hole 32is preferably positioned such that its center is between about 5 mm andabout 9 mm, preferably between about 6 and about 8 mm, and morepreferably about 6.5-7.5 mm perpendicularly and caudally from thesuperior hole 30 as shown by line 30-32 _(W).

The plate 10 has been described in its preferred embodiment as sized tobe used with medium to large canines. In that embodiment, the plate isdesigned to be preferably used with 3.5 mm bone screws and has a distalportion 12 width W of between about 9-14 mm, preferably about 10-13 mm.more preferably 11-12 mm.

The plate 10, however, can be adjusted to fit various anatomies. Forexample, the plate can be downsized to fit smaller animals, such assmaller canines. In such a smaller version, the plate can be designedfor its screw holes 16 to accommodate 2.7 mm bone screws. The width ofsuch a plate can be between about 5-10 mm, preferably 6-9 mm, and morepreferably 7-8 mm. For this sized plate, the radius 42 for the cylinder29 defining the bone-contacting surface 22 for the proximal portion 14of the plate is between about 13.5 and about 18 mm, preferably 14.5 and17 mm, and more preferably 15.5 and 16 mm. The first rotation axis 48for this sized plate can be located about 13 to about 21 mm, preferablybetween about 15 to about 19 mm, more preferably about 17 mm distallyfrom the center axis of the superior hole 30. The angles for rotationfor viewing the center axis of cylinder 29 perpendicular to the page arethe same for the first rotation as described above, but for the secondrotation the angle is between about 18-26°, preferably between about20-24°, and more preferably about 22°.

The smaller 2.7 mm plate can be designed to have its proximal portion 14screw holes located in a similar pattern as with the 3.5 mm plate. Asbefore, all screw hole dimensions are taken from the points defined bythe intersection of hole axis with the top surface of the plate asdepicted by axis points 35. As shown in FIG. 10, preferably the centerof cranial screw hole 31 will be positioned a distance of between about2 mm and about 4 mm, preferably about 2.5 mm to about 3.5 mm, and morepreferably about 3 mm distally from superior hole 30 and parallel tomid-plane 44 as shown by line 30-31 _(L). Also preferably, the center ofcaudal screw hole 32 will be positioned a distance of between about 4 mmto about 7 mm, preferably about 5.5 mm to about 6.5 mm, and morepreferably about 5-6 mm distally from superior hole 30 and parallel tomid-plane 44 as shown by line 30-32 _(L). The head portion 14 screwholes can also be positioned off-set from the mid-plane 44. Superiorscrew hole 30 can have its center positioned either on the mid-plane 44,or preferably it is positioned between about 0 mm and about 2.5 mm,preferably about 0 and about 1.5 mm, and more preferably about 0.5 mmperpendicularly and cranially from the mid-plane 44 as shown by line 30_(W). The cranial screw hole 31 is preferably positioned such that itscenter is between about 2.5 mm and about 5.5 mm, preferably betweenabout 3.5 mm and about 4.5 mm, and more preferably about 3.7-4.3 mmperpendicularly and cranially from the superior hole 30 as shown by line30-31 _(W). The caudal screw hole 32 is preferably positioned such thatits center is between about 3 mm and about 6 mm, preferably betweenabout 4.5 and about 5.5 mm, and more preferably about 4-5 mmperpendicularly and caudally from the superior hole 30 as shown by line30-32 _(W).

In another embodiment, as shown in FIGS. 11-12, the plate 10 has adesign to accommodate a larger plate structure for use with largeranimals. The plate 10 has a distal portion 12 that is slightly wider,having a width between about 12 and about 15 mm, preferably betweenabout 12 and about 13.5 mm wide. The distal portion 12 can have morethan three screw holes and is shown here with four screw holes 16, twoof which are combination screw holes 16 a, however all of these holes 16can be either combination screw holes, oblong screw holes 16, conicalscrew holes, or any combination of conical, oblong or combination holes.The screw holes can be aligned with the mid-plane 44 of the plate 10 orsome or all can be off-set as depicted.

As shown in FIGS. 11-12, the proximal portion 14 can be designed toaccommodate various screw holes, here depicted as four screw holes.These screw holes can be for locking screws as described above. Again,the proximal portion 14 can be pre-bent to contour to the tibial bonesegment cut and rotated during the TPLO procedure. The location of thecylindrical surface defining the bone contacting surface 22 for theproximal portion 14 can be defined as above through the two angles ofrotation. The starting axis 48 for the rotation for this size plate canbe as described above, but located between about 25 and 38 mm,preferably between about 28 and about 35 mm, more preferably about 31-32mm distally from the center axis of the superior hole 50. The firstrotation can be in the same amount as described above, and the secondrotation can be between about 10-25°, preferably between about 15-20°,and more preferably about 18°. The radius 40 of the cylinder 29 can befrom about 20-32 mm, preferably about 23-29 mm, more preferably about25-27 mm.

The four screw holes in the proximal portion 12 can be defined as asuperior hole 50, a cranial hole 51, a caudal hole 52, and a distal hole53. These holes can also be located off of the plate mid-plane 44 andpreferably the superior hole 50 is located between 0 and 5 mm,preferably 1.5-4 mm, and more preferably 2-3 mm cranially from themid-plane 44. The cranial hole 51 can be located between about 3.5-11.5mm, preferably about 5.5-9.5 mm, and more preferably about 7-8 mmdistally from the superior hole 50 as shown by line 50-51 _(L). Thecaudal hole 52 can be located between about 5.5-13.5 mm, preferablyabout 7.5-11.5 mm, and more preferably about 9-10 mm distally from thesuperior hole 50 as shown by line 50-52 _(L). The distal hole 53 can belocated between about 5.5-13.5 mm, preferably about 7.5-11.5 mm, andmore preferably about 9-10 mm distally from the superior hole 50 asshown by line 50-53 _(L). The cranial hole 51 can be located betweenabout 2-10 mm, preferably about 4-8 mm, and more preferably about 5-7 mmcranially from the superior hole 50 as shown by line 50-51 _(W). Thecaudal hole 52 can be located between about 5.5-15.5 mm, preferablyabout 8-12 mm, and more preferably about 10-11 mm caudally from thesuperior hole 50 as shown by line 50-52 _(W). The distal hole 53 can belocated between about 0-4 mm, preferably about 1-3 mm, and morepreferably about 1.5-2 mm caudally from the superior hole 50 as shown byline 50-53 _(W).

The bone plate 10 can be used in a TPLO procedure as well known in theart. Generally, the tibia will be cut in a curved fashion and rotated.The cut and rotated portion can then be joined to the lower or distalportion of the tibia by use of the bone plate 10. The plate 10 can besecured to the distal and cut/rotated segments of the tibia by securingbone screws to the bone segments through the screw holes on the plate.The bone plate can be supplied with the mating screws in the form of akit.

The pre-contoured plate of the present invention provides variousbenefits. The plate is designed to be pre-fitted or contoured to thespecific bone anatomy. The plate is also designed such that after theproximal portion is pre-contoured, the screw holes for the proximalportion are machined through the plate. These screw holes are preferablydesigned for use with locking screws. When the locking screws aresecured through the plate and into the tibial bone segment, their screwpath is pre-targeted to advantageously avoid the articular surfacebetween the tibia and the femur, to avoid the osteotomy surface, and toavoid the outer edge or surface of the tibia.

The targeted nature of the screw paths for the screws in the proximalportion 14 of the plate 10 is depicted in FIGS. 13-14. As shown in FIG.13, the superior screw 30 a is designed to have a targeted screw paththat is angled downward slightly, distally, away from the articularsurface 60 between the proximal, cut segment 66 of the tibia 64 and thefemur 68. The superior screw 30 a is also shown as being angled slightlycaudally to avoid the outer edge 70 of the tibia. The cranial screw 31 ais shown as being angled slightly caudally toward the center of thetibia and away from the osteotomy edge 62 of the tibia. The caudal screw32 a is shown as being angled slightly cranially toward the center ofthe tibia and away from the outer edge 70 of the tibia. As shown in FIG.14, the plate 10 is secured to the distal portion of the tibia 64 and tothe osteotomy cut segment 66 of the tibia.

What is claimed:
 1. A bone plate dimensioned for securing two tibialbone segments of an animal as part of a tibial leveling osteotomyprocedure for an animal, the bone plate comprising: a distal portioncomprising an elongated shaft having disposed therein a plurality ofdistal portion screw holes each designed to accept a screw and defininga longitudinal axis and a base plane along a bone-contacting surfacethereof; a proximal portion having an upper surface and abone-contacting surface opposite the upper surface, the bone-contactingsurface of the proximal portion being pre-configured and dimensioned toconform to a tibial bone segment and having a contour formed as an arcof a cylinder having a contour axis extending in a plane including afirst rotation axis defined by an intersection of a mid-plane and atransverse plane and rotated relative to the mid-plane about the firstrotation axis by a first angle, the mid-plane bisecting the base plane,and the transverse plane being orthogonal to the mid-plane and the baseplane, and wherein the axis is rotated relative to a second rotationaxis defined by an intersection of the transverse plane and the baseplane by a second angle; a plurality of proximal portion screw holeslocated in the proximal portion that were machined through thepre-contoured bone-contacting surface, the proximal portion screw holesbeing designed to accept a locking screw, whereby locking screwsanchored through the proximal portion screw holes will have a targetedscrew path through the tibial bone segment.
 2. The bone plate of claim 1wherein the proximal portion has a first screw hole that is designed toaccept a first locking screw that has a targeted screw path that anglesaway from the bone-contacting surface of the proximal portion in adistal direction.
 3. The bone plate of claim 2 wherein the screw pathfor the first locking screw also angles caudally away from thebone-contacting surface.
 4. The bone plate of claim 2 wherein theproximal portion has a second screw hole that is located distally andcranially from the first screw hole and is designed to accept a secondlocking screw that has a targeted screw path that angles caudally awayfrom the bone-contacting surface.
 5. The bone plate of claim 2 whereinthe proximal portion has a second screw hole that is located distallyand caudally from the first screw hole and is designed to accept asecond locking screw that has a targeted screw path that anglescranially away from the bone-contacting surface.
 6. The bone plate ofclaim 1 wherein the first screw hole is a superior screw hole and theproximal portion has a cranial screw hole that is located distally andcranially from the first screw hole and is designed to accept a craniallocking screw that has a targeted screw path that angles caudally awayfrom the bone-contacting surface, and the proximal portion has a caudalscrew hole that is located distally and caudally from the first screwhole and is designed to accept a caudal locking screw that has atargeted screw path that angles cranially away from the bone-contactingsurface.
 7. The bone plate of claim 6 wherein the screw path for thesuperior screw hole also angles caudally away from the bone-contactingsurface.
 8. The bone plate of claim 7 wherein the bone-contactingsurface is contoured in the shape of a cylinder.
 9. The bone plate ofclaim 8 wherein the radius of the cylinder that defines at least part ofthe bone-contacting surface of the proximal portion of the plate isbetween about 18 mm and about 24 mm.
 10. The bone plate of claim 8wherein the radius of the cylinder that defines at least part of thebone-contacting surface of the proximal portion of the plate is betweenabout 22 mm and about 30 mm.
 11. The bone plate of claim 8 wherein theradius of the cylinder that defines at least part of the bone-contactingsurface of the proximal portion of the plate is between about 12 mm andabout 20 mm.
 12. A bone plate for securing two tibial bone segments aspart of a tibial leveling osteotomy procedure for an animal, the boneplate comprising: a distal portion comprising an elongated shaft havingdisposed therein a plurality of screw holes each designed to accept ascrew; and a proximal portion comprising at least three screw holes eachdesigned to accept a screw wherein a first screw hole is a superiorscrew hole, a second screw hole is a cranial screw hole located distallyand cranially from the superior screw hole, and a third screw hole is acaudal screw hole located distally and caudally from the superior screwhole, wherein screw hole paths for the at least three screw holes arepredetermined and angled so as to direct screws away from an articularsurface between a tibia and a femur, away from an osteotomy surface ofthe tibia, and away from edges of the tibia and into a central mass ofthe tibia.
 13. The bone plate of claim 12 wherein the cranial screw holeis located between about 3.5 mm and about 6 mm distally from thesuperior screw hole and the caudal screw hole is located about 6 mm toabout 9 mm distally from the superior screw hole.
 14. The bone plate ofclaim 13 wherein the superior screw hole, the cranial screw hole, andthe caudal screw hole are each designed to accept a locking screw. 15.The bone plate of claim 12 wherein the cranial screw hole is locatedbetween about 2 mm and about 4 mm distally from the superior screw holeand the caudal screw hole is located about 4 mm to about 7 mm distallyfrom the superior screw hole.
 16. The bone plate of claim 15 wherein thesuperior screw hole, the cranial screw hole, and the caudal screw holeare each designed to accept a locking screw.
 17. The bone plate of claim12 wherein the cranial screw hole is located between about 5.5 mm andabout 9.5 mm distally from the superior screw hole and the caudal screwhole is located about 7.5 mm to about 11.5 mm distally from the superiorscrew hole.
 18. The bone plate of claim 17 wherein the superior screwhole, the cranial screw hole, and the caudal screw hole are eachdesigned to accept a locking screw.
 19. A method for performing a tibialplateau leveling osteotomy procedure, comprising: fixing a first tibialsegment having an outer surface to a second tibial segment having anouter surface by securing a bone plate to the outer surface of the firstand second segments, wherein the bone plate comprises a distal portioncomprising an elongated, shaft having disposed therein a plurality ofdistal portion screw holes each designed to accept a screw and defininga longitudinal axis and a base plane along a bone-contacting surfacethereof; a proximal portion having an upper surface and abone-contacting surface opposite the upper surface, the bone-contactingsurface of the proximal portion being pre-configured and dimensioned toconform to the outer surface of the first tibial bone segment and havinga contour formed as an arc of a cylinder having a contour axis extendingin a plane including a first rotation axis defined by an intersection ofa mid-plane and a transverse plane and rotated relative to the mid-planeabout the first rotation axis by a first angle, the mid-plane bisectingthe base plane, and the transverse plane being orthogonal to themid-plane and the base plane, and wherein the axis is rotated relativeto a second rotation axis defined by an intersection of the transverseplane and the base plane by a second angle; a plurality of proximalportion screw holes located in the proximal portion that were machinedthrough the pre-contoured bone-contacting surface, the proximal portionscrew holes being designed to accept a locking screw, whereby lockingscrews anchored through the proximal portion screw holes will have atargeted screw path through the first tibial bone segment.
 20. A kit fora tibial plateau leveling osteotomy procedure comprising: (1) a boneplate dimensioned for securing two tibial bone segments of an animal aspart of a tibial leveling osteotomy procedure for an animal, the boneplate comprising: a distal portion comprising an elongated shaft havingdisposed therein a plurality of distal portion screw holes each designedto accept a screw and defining a longitudinal axis and a base planealong a bone-contacting surface thereof; a proximal portion having anupper surface and a bone-contacting surface opposite the upper surface,the bone-contacting surface of the proximal portion being pre-configuredand dimensioned to conform to a tibial bone segment and having a contourformed as an arc of a cylinder having a contour axis extending in aplane including a first rotation axis defined by an intersection of amid-plane and a transverse plane and rotated relative to the mid-planeabout the first rotation axis by a first angle, the mid-plane bisectingthe base plane, and the transverse plane being orthogonal to themid-plane and the base plane, and wherein the axis is rotated relativeto a second rotation axis defined by an intersection of the transverseplane and the base plane by a second angle; a plurality of proximalportion screw holes located in the proximal portion that were machinedthrough the pre-contoured bone-contacting surface, the proximal portionscrew holes being designed to accept a locking screw, whereby lockingscrews anchored through the proximal portion screw holes will have atargeted screw path through the tibial bone segment; and (2) lockingbone screws adapted to fit within the proximal portion screw holes.